1. Field of the Invention
The present invention relates to sound field reproducing apparatus and method for reproducing reflections and, more particularly, to sound field reproducing apparatus and method for reproducing reflections to provide realistic presence and space perception to audiences by reproducing reflections using a panning algorithm or reproducing reflections using each of loudspeakers while reproducing not only a direct sound but also the reflect sources in a surround sound field through multichannel loudspeakers.
This work was supported by the IT R&D program of MIC/IITA [2007-S-004-01, “Development of Glassless Single-User 3D Broadcasting Technologies”].
2. Description of Related Art
Three dimensional (3-D) sound source reproduction technologies have been advanced from stereophony to discrete surround, binaural reproduction, or transaural reproduction. Although sound source reproduction schemes such as 2 channel stereo, 5.1 channel surround, or 7.1 channel surround, provide a sound image that enables audiences to have 3-D effect, these schemes have shortcoming of a limited listening sweet spot.
In order to overcome such a shortcoming, a wave field synthesis (WFS) reproduction technology was introduced. The WFS reproduction technology is a technology for reproducing not only a spherical wave sound field but also a plane wave sound field. Also, the WFS reproduction technology has many advantages, for example, reproducing a moving sound source and forming a virtual sound source any locations in a listening area. Therefore, the WFS reproduction technology has been receiving attention as next generation audio reproduction technology.
In 3-D sound source reproduction technology, processing sound field is one of important parts for providing realistic space perception and presence to audiences. For example, an artificial reverberator, a sound field reproducing device, processes such a signal that gives realistic space perception and presence to audiences. It is an object of the sound field reproducer to change a sound environment in a listening room to a desired sound environment for audiences. But, a sound environment of home may be partly compensated through a sound field tuning system.
However, it is necessary to process a sound field signal to artificially form an optimal sound environment according to a sound source. Such a sound field reproducing technology must employ a signal processing scheme different from that of the reverberator. Most of sound sources include reverberation components. If reverberation is input to a sound field reproducer, reverberation time is lengthened because reverberation overlaps in a sound source. Therefore, a sound tone is distorted.
In case of a movie sound source, new approach is required for processing a sound field thereof because a sound field effect is maximized by controlling frequency characteristics, instead of reverberation, according to movie genres. Therefore, a sound field reproduction technology for home theater depends on experience and artistry, not theory.
Currently, there is no standard introduced for an optimal reproducing apparatus or for recording, which can be applied to a wave field synthesis reproducing environment. It is essential to reproduce a surround sound field recording sound source in a wave field synthesis reproducing environment in a view of backward compatibility. That is, a sound field reproducing function is essentially required to change a desired sound environment for audiences.
In order to satisfy such a requirement, many researches have been made for realizing virtual sound image localization by reproducing only direct sound based on a wave field synthesis rendering scheme. A sound field reproducing scheme according to the related art does not perform signal processing or reproduces additionally obtained audio as it is. For example, a sound reproducing system according to the related art introduced by a ‘Delft’ university records each of sound sources with almost no echo through spot microphones in a recording studio. Then, the sound reproducing system localizes the recorded sound sources at predetermined locations as virtual sound sources through a wave field synthesis rendering method at a reproducing end. The sound reproducing system records reverberation and reflections in a recording studio through stereo microphones and renders the recorded sounds as virtual stereo sound sources farther away therefrom.
However, according to the sound reproducing technology, a complete wave field synthesis reproducing system only can be realized through a wave field synthesis rendering and direct recording anechoic sound sources. That is, the sound reproducing technology according to the related art cannot embody a complete wave field synthesis reproducing system through other sound source.
Particularly, a wave field synthesis reproducing technology using a multichannel loudspeaker array considers all of sound sources to reproduce as point sources. Such a wave field synthesis reproducing technology produces audio by processing signals using information about a reproducing direction, a time, and a size of sound sources for an audience location.
In order to reproduce a sound source in a predetermined space, it is necessary to reproduce not only a direct sound of the sound source but also reflections generated from walls, floors, and ceiling for providing realistic audio to audiences. That is, if a wave field synthesis reproduction method is used for processing the reflections as well as for the direct sound, it is possible to provide further realistic the presence and the space perception to audience.
However, there may be about several thousands to ten thousands of reflections that characterize a predetermined space. Therefore, if all of reflections are processed through the wave field synthesis reproduction method, computation amount and time increase. That is, the wave field synthesis reproduction technology using a multichannel loudspeaker array according to the related art has difficulties to process reflections through the wave field synthesis reproduction method. Thus, the wave field synthesis reproduction technology cannot maximize presence and space perception.